Site Selection
It is important to focus on elevation relative to the tide changes over time when determining sites for TLP . Some key factors of site selection are short fetch , low wave energy , gentle slope of 1-3 %, and ability for the system to mitigate sea level rise through natural processes or human interventions ( Myszewski , 2017 ). Priority should be placed on sites where sediment inputs are lacking and elevation has been lost . Another area of interest would be where sea level rise is happening too quickly or has already had too big of an impact to allow the natural environment to accumulate the sediment back . Below is a general overview of suitable conditions for TLP :
›››› Low wave energy
›››› Gentle slopes with 1-3 % grade
Materials and Preparation
It is important to determine what type of sediment should be chosen to use as the fill material . Traditionally , subaqueous sediment is dredged from nearby estuarine streams to be used as cap material for TLP . Cap materials are typically composed of sand , sediment , or gravel ( Merrit et al ., 2010 ), with sandy silt soils being the dominant sediment type in the Kiawah River . The use of native soils allows for a faster and better natural recovery process . Understanding the multi-dimensional sediment budget within a local estuarine system is critical for determining the long-term success and sustainability of projects which alter sediment dynamics ( Ganju , 2019 ). Dredging materials from the stream beds may result in further deterioration of the marsh platform as sediments in the area gradually reach an equilibrium . The chance for this occurring is increased if external sediments are not deposited in the borrow site .
Encouraging vertical accretion through TLP may result in lateral erosion along marsh banks . It is also recommended to monitor water quality for sulfur , ammonium , heavy metals , and other naturally occurring nutrients introduced by borrowed soils which can impact the local ecosystem ( VanZomeren and Piercy , 2020 ). Introduction of hydrogen sulfides from subaqueous sediments may result in vegetative loss within treatment sites ( VanZomeren and Piercy , 2020 ).
Sediment control devices ( i . e ., coir logs ) should be incorporated alongside TLP to trap eroded sediment and prevent horizontal erosion along stream banks .
Installation
Before installation , it is recommended to remove any barriers , ditches , and depressions from the treatment site . TLP uses a modification of existing hydraulic dredging methods in which sediments are hydraulically dredged , liquefied , and then pumped through a pressurized spray nozzle ( Ray , 2007 ). This can be done through low-pressure or highpressure applications ( Myszewski et al ., 2017 ). Low pressure hydraulic dredging softens and liquifies sediments before application . Low pressure applications usually result in heavier sediments ( e . g ., sand , shell hash , and gravel ) being deposited nearest to the discharge point . This can result in an unequal distribution of sediments and create uneven topography .
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NATURE-BASED SOLUTIONS MANUAL FOR KIAWAH ISLAND